Eye, nose and throat irritation (trigeminally mediated sensations) comprise the most frequently reported acute symptoms among individuals exposed to environmental tobacco smoke and in so-called "problem buildings." Marked variation in individual sensitivity to airborne irritants has been reported epidemiologically and clinically, with some observers linking nasal reactivity to irritants with pre-existing allergic rhinitis. Although irritant-associated symptoms such as nasal congestion and rhinorrhea may mimic an allergic response, experimental studies using chemical irritants have not documented allergic mechanisms; instead, neurogenic reflexes have been implicated. The goal of this series of experiments is to address the following questions: 1) Do individuals with allergic rhinitis have more sensitive nasal irritant perception than nonrhinitic subjects? 2) Do individuals with allergic rhinitis have greater physiological reactivity to irritant stimuli (i.e., changes in nasal airway resistance and nasal mucosal blood flow) than do non-rhinitics? and 3) Are non-allergic mechanisms (autonomic or axon reflexes) apparent in the acute irritant response of either rhinitics or non-rhinitics? These questions will be addressed with a series of randomized, cross-over design environmental challenge studies comparing subjects' response to filtered air with their response to a 15-minute exposure to chlorine gas (Cl2) at 1.0 part-per-million administered via nasal mask in a climate controlled chamber. Subject panels will consist of 32 non-smoking, non-asthmatic individuals (frequency matched on gender and age), half with allergy skin-test confirmed seasonal allergic rhinitis, and the other half without; allergic subjects will be studied "out-of-season." Separate studies will examine the effect of Cl2 vs. air on: 1) nasal airway resistance, 2) nasal mucosal blood flow, and 3) nasal lavage fluid concentrations of albumin, lysozyme, and substance P. In each experiment, control exposures (filtered air) will occur on separate days and in random order. Exposure-related physiologic and biochemical changes will be analyzed using ANOVA for repeated measures. Selected trials will be repeated after pre-treatment with a topical cholinergic blocker (ipratropium bromide). Physiologic reactivity (above) will be compared with nasal irritant perceptual acuity, as measured with a discrimination task involving pulsed CO2 and filtered air.